Synthesis of 6-Hydroxy-2-methyl-3-thioxo-2H-1,2,4-triazin-5-one

The title compound has been prepared in three steps from 2-methylthiosemicarbazide following acylation, cyclisation and cation exchange chromatography. It was fully characterised by the usual spectroscopic means as well as by ¹⁵N nmr spectroscopy and X-ray crystallographic analysis.     

Differential Recognition of Anions with Selectivity towards F− by a Calix[6]arene–Thiourea Conjugate Investigated by Spectroscopy,Microscopy, and Computational Modeling by DFT

Anion recognition studies were performed with triazole‐appended thiourea conjugates of calix[6]arene (i.e., compound ⁶ L ) by absorption and ¹H NMR spectroscopy by using nineteen different anions. The composition of the species of recognition was derived from ESI mass spectrometry. The absorption spectra of compound ⁶ L showed a new band at λ=455 nm in the presence of F^? due to a charge transfer from the anion to the thiourea moiety and the absorbance increases almost linearly in the concentration range 5 to 200 μm . This is associated with a strong visual color change of the solution. Other anions, such as H₂PO₄^? and HSO₄^?, exhibit a redshift of the λ=345 nm band and the spectral changes are associated with the formation of an isosbestic point at λ=343 nm. ¹H NMR studies further confirm the binding of F^? efficiently to the thiourea group among the halides by shifting the thiourea proton signals downfield followed by their disappearance after the addition of more than one equivalent of F^?. The other anions also showed interactions with compound ⁶ L , however, their binding strength follows the order F^?>CO₃^2?>H₂PO₄^?≈CH₃COO^?>HSO₄^?. The NMR spectral changes clearly revealed the anion‐binding region of the arms in case of all these anions. The anion binding to compound ⁶ L indeed stabilizes a flattened‐cone conformation as deduced based on the calix‐aromatic proton signals and was further confirmed by VT ¹H NMR experiments. The stabilization of the flattened‐cone conformation was further augmented by the interaction of the butyl moiety of the nBu₄N⁺ counterion. The structural features of the anion‐bound species were demonstrated by DFT computations and the resultant structures carried the features that were predicted based on the ¹H NMR spectroscopic measurements. In addition, SEM images showed a marigold flower‐type morphology for compound ⁶ L and this has been transformed into a chain‐like structure of connected spherical particles in the presence of F^?. The anion‐induced microstructural features are reflective of the binding strength, size, and shape of the anions. The binding strengths of the anions by compound ⁶ L were further compared with that of compound ⁴ L , a calix[4]arene analogue of compound ⁶ L , in order to address the role of the number of arms built on the calixarene platform based on absorption spectroscopy, ¹H NMR spectroscopy, and DFT computations and it was found that compound ⁶ L is a better receptor for F^?, which extends its interactions from all the three arms.     

Diastereoselective synthesis of (+)-nephrosterinic acid and (+)-protolichesterinic acid

A diastereoselective synthesis of (+)-nephrosterinic acid and (+)-protolichesterinic acid, common members of the paraconic acids is described. The synthesis is based on a diastereoselective orthoester Johnson–Claisen rearrangement of a (Z)-allyl alcohol with a vicinal dioxolane moiety as key steps. The synthesis is completed in 10 steps and with overall yields of 15.9% for (+)-nephrosterinic acid and 16.4% for (+)-protolichesterinic acid.     

Polyaniline-Anchored Metal Salts for Michael Reaction of α,β-Unsaturated Ketones

A catalyst consisting of polyaniline-anchored metal salts is used as a Lewis acid to promote the Michael reaction of α,β-unsaturated ketones. The reaction is performed efficiently with imidazole, acetyl acetone, and ethyl acetate as Michel donors and chalcones as the acceptors under ultrasound irradiation.     

Silica–Sulfuric Acid Catalyzed Nitrodeiodination of Iodopyrazoles

Abstract

We report here the synthesis of nitropyrazoles in good to excellent yields from iodopyrazoles over silica–sulfuric acid catalyst for the first time. The present procedure require less acid, offers a simplified workup procedure, and may be applied for the nitration of a wide variety of iodoazoles in drug and pharmaceutical industries.     

Reductive Studies on 3-Oxidopyrylium-alkene [5 + 2] Cycloadducts: Access to Some Hydroxy Cycloheptenoids

The scope of nickel boride as a versatile reducing reagent is extended to the 3-oxidopyrylium-alkene [5 + 2] cycloadducts. In this report, we demonstrate that nickel boride is capable of one-pot 1,2- and 1,4-reduction of enones present in the cycloadducts in good yields. Subsequent elaboration of the cycloadducts towards synthesis of functionalized cycloheptenoid derivatives devoid of the oxa-bridge is also explored.